The invention relates to a method of sealing a reactor pressure vessel (RPV) and, more particularly, to a method for temporarily sealing a RPV submerged under twenty feet of water or more.
Commercial nuclear reactors for generating electrical power must be taken off-line every one to two years in order to refuel the reactors. During such refuelings and other scheduled outages when the RPVs must be opened, the refueling cavities are flooded with water to depths of twenty (20) feet or more above the RPV circumferential flanges so that their removable upper heads may be safely removed. During such outages, periodic inspections, maintenance activities and repairs may be performed on the RPVs and/or on associated vessels and equipment such as steam generators, coolant circulating pumps and the like as well as the interconnecting piping. Certain of these inspections and other activities must be performed on dry surfaces. Accordingly, the RPVs or the balance of the loops must be sealed from the pools so that the loops can be at least partially drained.
Temporary RPV heads have been designed to replace removed RPV heads in order to provide a seal between the internal portions of the RPVs (and the balance of the loops) and the pools of water in which the RPVs are submerged. These temporary RPV heads are large and heavy and expensive, special handling equipment is needed to transport them. It is desirable to employ existing on-site RPV internals lifting rigs to transport the temporary RPV heads and to guide them into position on RPV flanges. Such RPV internals lifting rigs are supported on the RPVs and normally used for transporting and positioning internal assemblies and fuel rod assemblies in the RPVS. However, the weight and/or the structural elements of the temporary RPV heads must be compatible with the lifting capabilities and/or structure of the existing lifting rigs if they are to be precisely positioned on the RPV flanges.
The temporary RPV head designs may have pumping devices carried by their domed portions. These devices pump out water which may leak into the RPVs if the temporary RPV heads are not precisely positioned on the RPV flanges by the lifting rigs. Undesirably, such devices complicate the structure and use of the temporary RPV heads.